Hi Ed
Yes, the Prince heads are two plug. It has been suggested to me that there is zero advantage in having two spark plugs firing, but from my reading that is not the case. If you take your standard new Porsche back to the Porsche factory for a power upgrade, they insist on changing to a twin plug ignition. The main purpose of this change is to eliminate the detonation which would surely happen with single plug ignition and a boosted compression ratio. The two plug ignition allows the timing to be pulled back about 5 degrees or more. Additionally, the two flame fronts add three to five percent to the power band. The extra power is greatest with engines which use a domed piston (Vincent) to acheive a high CR.
Another feature of the Prince heads are the generous squish bands designed into the combustion chambre. Drag racers call this type of head a "quench head" because the squish area cools the combustion chamthisbre if set up with proper very tight clearances. This effect also aids in preveion of detonation while adding a lot of hp, particularly in the midrange.
Terry has also added a lot of fin area to give more cooling, again